On Wed, 02 Nov 2011 13:18:20 -0500, Paul Remde wrote:

I suspect that the iPAQ's battery was low. The hx4700 draws only about
300 to 400 mA when the battery is fully charged. But it can draw well
over 1 A when the battery is low. The 302 would probably work fine if
you connected the hx4700 to it when the battery was fully or nearly
fully charged.

I'd agree. I have an ancient iPAQ 3630 which specifies that its 5v
connection can draw up to 1.4 amps from a charger or whatever. As it is
supposed to run for 3 hours from a full charge and has an 800 mAh
battery, that implies that it uses around 270 mA during normal operation.

Its also worth remembering that the USB 2.0 spec says a connection should
be rated for 800 mA - and there are some devices that will try to draw
more than that. However, it would be wise to size the Mio power supply
for at least 1.5 amps[1] rather than 0.4 amps because at some point
Murphy guarantees you *will* connect the Mio with with an almost fully
discharged battery.

For what its worth, I bought a cheap 12v charging cable off eBay for my
iPAQ and took it apart. The cigar-lighter end contains a very small
12v - 5v converter rated at 1.5 amps. I installed it in a small metal
box (these small switch-mode voltage converters may stick out a lot of RF
hash) and permanently wired its 12v side to the glider battery. I have
lots of bad experiences with those cigar lighter plugs leaping out of the
socket for no apparent reason, so wasn't going to risk using one: besides
they are very bulky. The iPAQ is long retired, but I'm still using the
voltage adapter, which has to date powered the iPAQ 3630, a Garmin GPSII+
and, currently, my Binatone B.350 PNA.

[1] or the Mio's rated max input current, whichever is largest.


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martin@ | Martin Gregorie
gregorie. | Essex, UK
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